I very much enjoyed the book despite agreeing with some of the specific accusations that other reviewers level at it.
Specifically, there are three faults:
(a) the plot is far-fetched,
(b) there's too much Ellie Pascoe, surely the most irritating coffee-table socialist ever created,
(c) there's the usual tendency towards overwrought writing, arcane vocabulary and general pretentiousness. This has always been the case with Reginald Hill's books, but has become exaggerated with time. Arms and Women is a later period novel.
So why have i given it 4 stars? Well, it's just a really good read! Once you sign up to the story's fantastical premise, you never really look back. I hardly put the book down once i'd begun.
And really, if overwritten prose is a turn-off for you, then you shouldn't be reading Reginald Hill in the first place should you? Try Tess Gerritsen instead. No, this is for those who enjoy rich fare, at least now and again.